That would be the helmet that has a radio receiver installed in it, allowing the player to get instructions and calls from the coaches. And, as one might guess, it has a green dot on it.

For the past two seasons, Willis was the defensive player on the 49ers to wear the green dot - but the coaches figured that Willis has enough to do at middle linebacker as it is, so passing the Green Dot to Goldson at free safety might enable Willis to play faster, freed from the duty of relaying defensive signals to his 10 teammates.

"I feel the move this week will be good for us," Willis said. "If it does, I'm all for it. It's the small things. DBs like to hear that, making their calls on the back end. It's good for them to hear it."

The tipping point was Sunday in Houston. A second-quarter defensive lapse allowed Texans tight end Owen Daniels to get behind coverage on a 42-yard touchdown catch.

Based on the formation the Texans used, San Francisco's defensive coaches had an inkling about what was coming, but the call was late and didn't make it from the field to Willis' helmet to the secondary.

"They (the coaches) knew a shot was coming," Goldson said of Matt Schaub's pass to Daniels all by his lonesome. "We didn't get that. The little things like that, the dot will help us."

Having the defensive backs get the calls before Indianapolis quarterback Peyton Manning is finished with his famous presnap gesticulations is vital for the 49ers if they are to have a fighting chance against the Colts' No. 1-ranked passing offense.

"It's one less thing that Pat will have to think about," coach Mike Singletary said. "If there's a mistake back there (the secondary), nine times out of 10 it's going to reveal itself on the scoreboard. If it's on the back end, it's hard to recover."

Even by his exalted standards, Manning is having a career year. He's completing 72.6 percent of his passes, highest of his dozen years with the Colts. He has 15 TD passes against four interceptions and gets a lot of mileage out of five pass-catching pals: wide receiver Reggie Wayne(39 catches, 542 yards, 5 touchdowns), tight end Dallas Clark (38-485-3), running back Joseph Addai (27-156-1), rookie wideout Austin Collie (24-264-4) and second-year wideout Pierre Garcon(14-240-2).

"He's a future Hall of Famer," cornerback Shawntae Spencer said. "We played one of those earlier this year (Minnesota's Brett Favre). It's a little different because he runs his show. He calls his plays on the field. He's like a coach on the field."

Ulbrich considers future: Though putting off the official subject of retirement until after the season, linebacker Jeff Ulbrichsaid that going on injured reserve after his most recent concussion was the right thing to do.

Ulbrich spoke to reporters Wednesday for the first time since the 49ers put him on IR because of a concussion he sustained on the opening kickoff of the Rams game on Oct. 4.

"It's the right thing," a subdued Ulbrich said. "I'm OK with it. I feel really good. I missed the locker room. It's good to be back."

Ulbrich will help the 49ers where he can the rest of the season. He said his future plans include coaching.

"It was a combination of what the doctors said and not being able to play anymore," he said. "Lots to take in. I don't want to get into it. Not being able to play is hard. I love to play. Some guys play for money or fame. I never would have told Terry Donahue or Scot (McCloughan) or whoever the general manager was at the time that I would have played for very little, but I would."

Meanwhile: The 49ers' other player with concussion issues, strong safety Michael Lewis, has been cleared to play. He'll start Sunday in Indianapolis.

Cornerback's new deal: Although he has played very little this season, cornerback Tarell Brown received a three-year contract extension from the 49ers that will carry him through the 2013 season.

ESPN reported the extension is worth $7.125 million, with $2.5 million coming in a signing bonus.

Briefly: It's back to right tackle for flip-flopping Adam Snyder. One week after being shifted to right guard, he's back at tackle now that Tony Pashos is on injured reserve. Chilo Rachalremains at right guard. "Didn't last long, did it?" Snyder said of the move to guard. "I've done this before. It's not a big deal." ... The 49ers signed tackle Chris Patrick off Kansas City's practice squad. He'll back up Snyder. ... Singletary said wide receiver Brandon Jones, signed for $5.4 million in the offseason, will be active Sunday. ... Linebacker Takeo Spikes(shoulder) did not practice Wednesday.